Phosphate base laser glasses

ABSTRACT

A phosphate base laser glass comprising 55-70% P 2  O 5 , 1-15% Al 2  O 3 , 0-25% Li 2  O, 0-25% Na 2  O, 0-8% K 2  O, the total proportion of Li 2  O, Na 2  O, and K 2  O being 10-25%, 0-15% BaO, 0-15% ZnO, 0-15% CaO, 0-15%, SrO, 0-15% MgO, the total proportion of BaO, ZnO, CaO, SrO, and MgO being 5-15%, 0-5% Y 2  O 3 , 0-5% La 2  O 3 , 0-5% GeO 2 , 0-5% CeO 2 , 0-3% Nb 2  O 5 , 0-3% MnO 2 , 0-2% Ta 2  O 5 , 0-1% Sb 2  O 3 , and 0.01-5% Nd 2  O 3 , all % being mole %. 
     The phosphate base laser glass of this invention has a high induced emission cross section, a low non-linear refractive index coefficient, and excellent acid resistance and divitrification resistance. By replacing partially or wholely one or more of LiO 2 , Na 2  O, K 2  O, BaO, ZnO, CaO, SrO, MgO or Al 2  O 3  by LiF, NaF, KF, BaF 2  ZnF 2 , CaF 2 , SrF 2 , MgF 2  or AlF 3 , respectively, the above properties of the laser glass are further improved.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a phosphate base laser glass, and, more particularly, it relates to a phosphate base laser glass possessing a high induced emission cross section, a low non-linear refractive index coefficient, and excellent acid resistance and devitrification resistance.

2. Description of the Prior Art

Laser glasses for nuclear fusion have recently been required to have a high amplification factor and a low non-linear refractive index coefficient (the refractive index coefficient proportional to the square of the intensity of the electric field applied to the laser).

The amplification factor G of a laser is expressed by the equation

    G=e.sup.N·σ

wherein N is the inversion density and σ is the induced emission cross section. As is shown in the above equation, in order to increase the amplification factor G, the value of N·σ is required to be large, and, further, since the inversion density is determined by the input energy of a xenon flash lamp to the laser, it is desired as a characteristic of a laser glass that the induced emission cross section of the laser glass be as high as possible.

The refractive index of a laser in a high electric field is shown by the equation

    n=n.sub.o +n.sub.2 E.sup.2

wherein n₂ is the non-linear refractive index coefficient, E is the intensity of the applied electric field and n_(o) is the refractive index coefficient in a non-laser light (non-electric) field. If the non-linear refractive index coefficient is high, the laser light undergoes self-focusing to break the laser glass which makes the further use thereof difficult. Therefore, it is desired that a laser glass have a non-linear refractive index coefficient which is as low as possible. Phrased differently the lower the value of n₂, the stronger the power of the laser light can be. Generally, it can be used at a several G W/cm² for a nanosecond laser pulse and at a several hundred G W/cm² for a picosecond laser pulse. When n₂ is as low as possible, the laser glass does not break even when the upper limit of the power is high. However, in conventional silicate base laser glasses σ is 2.5-3.0×10⁻²⁰ cm² and n₂ is 1.5-2.0×10⁻¹³ e.s.u., and in conventional phosphate base laser glasses σ is 3.0-4.0×10⁻²⁰ cm² and n₂ is 1.5-2.0×10⁻¹³ e.s.u.

The laser glass disclosed in Japanese Patent Application Laid Open No. 114,615/'74 is a P₂ O₅ -alkali metal oxide-rare earth element oxide series laser glass containing a high proportion of rare earth element oxides, and the non-linear refractive index coefficient thereof is as high as 1.8-3.0×10⁻¹³ e.s.u. When used as a laser glass, the laser light causes self-focusing to break the laser glass and hence makes the further use thereof difficult. On the other hand, when rare earth element oxides in the laser glass are replaced with Al₂ O₃, the non-linear refractive index coefficient thereof becomes as high as 1.2-1.4×10⁻¹³ e.s.u., and thus breakage of the laser glass will not occur.

The present applicants previously filed a patent application on a P₂ O₅ -Li₂ O-Na₂ O-Al₂ O₃ series laser glass (Japanese Patent Application No. 134,788/'74). While this laser glass has a low non-linear refractive index coefficient n₂, it does not have excellent acid resistance and devitrification resistance due to the large proportions of Li₂ O and Na₂ O therein, which permits the utilization thereof as a laser rod.

SUMMARY OF THE INVENTION

One object of this invention is to provide a phosphate base laser glass having a high induced emission cross section, a low non-linear refractive index coefficient, and excellent acid resistance and devitrification resistance.

Another object of this invention is to provide an improved phosphate base laser glass which can provide large laser rods and laser discs without being accompanied by the heretofore discussed problems of conventional laser glass compositions.

As the result of intensive research on laser glass compositions, the inventors discovered that the aforesaid objects of this invention can be attained effectively by the laser glass of the invention which has the following composition: a phosphate base laser glass comprising 55-70% P₂ O₅, 1-15% Al₂ O₃, 0-25% Li₂ O, 0-25% Na₂ O, 0-8% K₂ O, the total proportion of Li₂ O, Na₂ O, and K₂ O being 10-25%, 0-15% BaO, 0-15% ZnO, 0-15% CaO, 0-15% SrO, 0-15% MgO, the total proportion of BaO, ZnO, CaO, SrO, and MgO being 5-15%, 0-5% Y₂ O₃, 0-5% La₂ O₃, 0-5% GeO₂, 0-5% CeO₂, 0-3% Nb₂ O₅, 0-3% MnO₂, 0-2% Ta₂ O₅, 0-1% Sb₂ O₃, and 0.01-5% Nd₂ O₃, all percentages being molar and based upon the total moles of the glass components.

DETAILED DESCRIPTION OF THE INVENTION

As compared to conventional silicate and phosphate base laser glasses as discussed above, in the laser glass of this invention σ is 4.20-6.5×10⁻²⁰ cm.² and n₂ is 0.7-1.40×10⁻¹³ e.s.u., that is, the induced emission cross section of the laser glass of this invention is 60-100% higher than that of conventional laser glasses and the non-linear refractive index coefficient n₂ of the laser glass of this invention is 40-50% lower than that of conventional laser glasses.

The inventors succeeded in improving the acid resistance and devitrification resistance of the laser glass described in their earlier Japanese Patent Application No. 134,788/'74 by incorporating therein 5-15 mole percent BaO, ZnO, CaO, SrO, and/or MgO as RO components, and thus have provided a glass which can be used to form large laser rods and laser discs. The acid resistance weight loss (Da) of the laser glass of this invention is about 0.15% by weight (1/100 normal HNO₃ for 1 hour at 100° C.), which shows the excellent acid resistance of the laser glass of this invention. Furthermore, as to the devitrification resistance of the laser glass of this invention, the value of Tg/LT (where Tg is the transistion temperature and LT is the liquid phase temperature) is above 0.4. Accordingly, the laser glass composition of this invention can be used to provide laser rods and laser discs, for example, in the last one or two years glass laser systems for use in the nuclear fusion area as have come into demand.

According to a particularly preferred embodiment of this invention, there is further provided a phosphate base laser glass comprising 58-67% P₂ O₅, 4-10% Al₂ O₃, 9-15% Li₂ O, 4-10% Na₂ O, 0-12% CaO, 0-12% MgO, 0-12% CaF₂, 0-12% MgF₂, the total proportion of CaO, MgO, CaF₂, and MgF₂ being 5-12%, 0-3% Y₂ O₃, 0.2-0.8% Nb₂ O₅, and 0.2-1.5% Nd₂ O₃, all percentages being molar and based on the total moles of the glass components, as illustrated in Examples 2 and 63 shown below.

A laser glass having the above-described preferred composition possesses excellent characteristics, that is, the acid resistance weight loss Da of the laser glass is 0.15-0.17% by weight, the devitrification resistance Tg/LT is 0.470-0.485, the induced emission cross section σ is 4.50-5.20×10⁻²⁰ cm.², and the non-linear refractive index coefficient n₂ is 1.13-1.24×10⁻¹³ e.s.u., which show the excellency of the laser glass of this invention at four characteristic points.

Each component of the laser glass of this invention will now be explained in regard to the limitations on the amount thereof.

Each component of the laser glass of this invention will now be explained in regard to the limitations on the amount thereof.

If the amount of P₂ O₅ is higher than 70 mole %, the oxide component largely volatilizes off during melting to make it difficult to melt the component in a stable manner, while if the amount of P₂ O₅ is lower than 55 mole %, the acid resistance of the laser glass becomes poor.

If the amount of Al₂ O₃ is lower than 1 mole %, the acid resistance of the laser glass becomes poor, while if the amount of Al₂ O₃ is higher than 15 mole %, the induced emission cross section of the laser glass becomes small, the devitrification resistance of the laser glass becomes poor and it becomes difficult to stably melt such large proportions of the component.

The total amount of Li₂ O, Na₂ O, and K₂ O in the laser glass composition of this invention is defined to be 10-25 mole %. If the total amount thereof is lower than 10 mole %, the induced emission cross section of the laser glass becomes small, while if the amount thereof is higher than 25 mole %, the acid resistance and the devitrification resistance of the laser glass simultaneously become poor and it becomes difficult to uniformly melt such a large amount of the components.

Each of Li₂ O and Na₂ O may be incorporated in the glass composition in an amount of up to 25 mole %, and in this range if both are used it is preferred that the molar amount of Li₂ O be greater than the proportion of Na₂ O since in this case the viscosity of the melt becomes higher and the components tend to be molded easily.

K₂ O may be incorporated therein in an amount of up to 8 mole %, but if the amount of this component is higher than that value, the induced emission cross section of the laser glass becomes small.

Furthermore, the total amount of BaO, ZnO, CaO, SrO, and MgO employed in this invention is 5-15 mole % as defined above, and if the total amount thereof is lower than 5 mole %, the acid resistance as well as the devitrification resistance of the laser glass becomes poor, and it becomes difficult to melt these elements sufficiently. On the other hand, if the total proportion thereof is higher than 15 mole %, the induced emission cross section of the laser glass becomes small and at the same time the non-linear refractive index coefficient thereof becomes high, which results in an unsuitable laser glass. Each of these components may be added in an amount of 15 mole % so long as the total amount thereof is in the aforesaid range.

If the amount of CaO and/or MgO is higher than the amount of BaO, ZnO, and/or SrO, the non-linear refractive index coefficient of the laser glass tends to become lower, but since in this case the induced emission cross section of the laser glass tends to become smaller, the ratio of these oxide components may be suitably selected considering the relative merits of these properties.

The presence of each of Y₂ O₃ and La₂ O₃ up to 5 mole % is effective to improve the acid resistance and the devitrification resistance of the laser glass, but if the amount of either Y₂ O₃ or La₂ O₃ is over 5 mole %, the induced emission cross section of the laser glass becomes small, and, at the same time, the non-linear refractive index coefficient becomes high, which makes the glass composition unsuitable as a laser glass. While the total amount of Y₂ O₃ +La₂ O₃ can be up to 5 mol %, it is preferred that when Y₂ O₃ is used alone no more than 3 mol % be used.

Also, GeO₂ may be incorporated in the glass composition up to 5 mole % to improve the melting property of the components, but if the amount of GeO₂ is over this value, it causes a phase separation in the glass, which forms scattering centers for laser light which renders the employment of such a glass composition unsuitable for use as a laser glass.

The presence of CeO₂, Nb₂ O₅, MnO₂, and Ta₂ O₅ up to an amount of 5 mole %, 3 mole %, and 2 mole %, respectively, is effective to prevent the occurence of solarization i.e., when a laser glass is subjected to pumping using a xenon flash lamp, the laser glass turns brown due to ultraviolet light from the xenon flash lamp and gradually tends to reduce in capability to pass the pumping light, finally rendering pumping impossible, but if the amount of each component is over the recited value, the non-linear refractive index coefficient of the laser glass becomes higher, and thus the employment of such a large proportion of the component is unsuitable.

Furthermore, CeO₂ and MnO₂ form Ce³⁺ ions and Mn²⁺ ions, respectively, in the glass, which serve as a sensitizer for Nd³⁺ ions.

The presence of Sb₂ O₃ in an amount of up to 1 mole % is effective as a defoaming agent for the melt.

Also, if the proportion of Nd₂ O₃ is lower than 0.01 mole %, it becomes difficult to oscillate and amplify the laser glass at such amounts, while if the proportion of Nd₂ O₃ is over 5 mole %, it also becomes difficult to oscillate and amplify the laser glass due to density quenching of fluorescence. The optimum proportion of Nd₂ O₃ is from about 0.2% to 1.5 mole %.

Moreover, according to another embodiment of this invention, at least one of Li₂ O, Na₂ O, K₂ O, BaO, ZnO, CaO, SrO, MgO, and Al₂ O₃ may be partially or wholely replaced by the corresponding fluorine compounds, such as LiF, NaF, KF, BaF₂, ZnF₂, CaF₂, SrF₂, MgF₂, and AlF₃, respectively. This embodiment of the invention wherein the metal oxides are partially or wholly replaced by the metal fluorides as described above is quite effective, since in such case the non-linear refractive index coefficient of the laser glass can be reduced to 0.7-0.9×10⁻¹³ e.s.u.

Examples of laser glasses of this invention are illustrated in Table 1, in which each component is shown by mole percent. Also, the characteristics of each sample are shown in Table 1. In Table 1, n₂ is the non-linear refractive index coefficient of the laser glass, the units of which are ×10⁻¹³ e.s.u., σ is the induced emission cross section, the units of which are ×10⁻²⁰ cm.², Da is the acid resistance, the units of which are weight loss percent, and Tg/LT is the value of the transistion temperature (°C) divided by the liquid phase temperature (°C), which shows the extent of devitrification resistance. In addition, the character F added to the upper left corner of a figure in Table 1 means that the corresponding metal fluoride was used, where the cationic ratio in each replacement was constant, i.e., replacement of each component is as follows; Li₂ O→2LiF, Na₂ O→2NaF, K₂ O→2KF, BaO→BaF₂, ZnO→ZnF₂, CaO→CaF₂ , SrO→SrF₂, MgO→MgF₂, and Al₂ O₃ →2AlF₃. In this case, in the production of the laser glass, the metal fluoride was used instead of the metal oxide.

It should be noted that in order to determine the full composition of any laser glass formed in the following examples it is often necessary to refer to the three different run number designations in Table 1.

                                      TABLE 1                                      __________________________________________________________________________      No.                                                                              P.sub.2 O.sub.5                                                                    Al.sub.2 O.sub.3                                                                   Li.sub.2 O                                                                         Na.sub.2 O                                                                         K.sub.2 O                                                                          BaO ZnO CaO SrO                                         __________________________________________________________________________     1  60  8   13  7.4                                                             2  60  8   13  7.4             3                                               3  60  8   13  7.4         3                                                   4  60  8   13  7.4     3                                                       5  60  8   13  7.4                                                             6  60  13  13  7.4                                                             7  60  10  13  1.6 7.4             7                                           8  60  3   13  7.4 3               12                                          9  55  3   13  7.4         15                                                  10 55  3   13  7.4             15                                              11 60  3   13  7.4                 15                                          12 60  3   13  7.4                                                             13 60  F.sub.3                                                                            F.sub.13                                                                           F.sub.7.4                                                       14 65  5   13  7.2     5                                                       15 65  5   12.2                                                                               7       6                                                       16 65  6   11  6       7                                                       17 65  5   11  6       8                                                       18 65  4   11  6       9                                                       19 65  3   11  6       10                                                      20 65  2   11  6       11                                                      21 65  2   11  6       10                                                      22 60  1   25              5.2 5                                               23 60  1       25      3.8 2   5                                               24 60  2       25      5       4                                               25 60  4.3 5   4   1   15                                                      26 60  6   F.sub.12                                                                           2       F.sub.15                                                27 60  2   17  1.5     5   10                                                  28 65  2   F.sub.7                                                                            5.7     7   F.sub.7                                             29 65  6   15          3   5                                                   30 70  3   10  1       3.2     10                                              31 60  3   F.sub.12                                                                           F.sub.8 F.sub.6 F.sub.5                                         32 60  F.sub.8                                                                            F.sub.10                                                                           9       F.sub.7                                                 33 65  8   12          5.8                                                     34 60  2   25          5       4.1                                             35 65  3       20          5                                                   36 65  8   F.sub.11    F.sub.7                                                 37 70  F.sub.7                                                                            F.sub.6                                                                            7       4   1                                                   38 70  3   11  4       3   2                                                   39 70  F.sub.6                                                                            7   5       5.2                                                     40 70  5   14          7                                                       41 70  4   9   2               9                                               42 70  6   10          8                                                       43 65  6   11  6.2         9.8                                                 44 70  5   11  6.2         5.8                                                 45 65  7.8 13  7.2         5                                                   46 65  6   11  6           3   F.sub.7                                         47 65  6   11  6           10                                                  48 70  6   11  6           5                                                   49 68  5.8 11  6.2             F.sub.5                                         50 68  4   11  6.2             F.sub.5                                         51 70  5.8 11  6.2             F.sub.5                                         52 70  4   11  6.2             F.sub.5                                         53 70  2   11  7       6                                                       54 70  2   12  8       6                                                       55 70  1   12  8       6                                                       56 70  1   12  7       8                                                       57 67  6   8.2 9           F.sub.5                                             58 65  6   10  10.2        5                                                   59 65  6   10  10.2            F.sub.5                                         60 65  6   8.2 9       7                                                       61 65  6   8.2 9       F.sub.8                                                 62 65  6   13  7.2     5                                                       63 65  6   11  6.2             F.sub.7                                         No.                                                                               MgO Y.sub.2 O.sub.3                                                                    La.sub.2 O.sub.3                                                                   GeO.sub.2                                                                          CeO.sub.2                                                                          Nb.sub.2 O.sub.5                                                                   MnO.sub.2                                                                          Ta.sub.2 O.sub.5                                __________________________________________________________________________     1  10                  0.4                                                     2  7                   0.4                                                     3  7                   0.4                                                     4  7                   0.4                                                     5  7           3       0.4                                                     6  5                   0.4                                                     7                      0.4                                                     8              0.6     0.4                                                     9      3       2   0.4                                                         10     3       2   0.4                                                         11         0.6     0.4                                                         12 15      0.6     0.4                                                         13 F.sub.15                                                                               0.6     0.4                                                         14     2.8             0.8                                                     15                 3.6                                                         16         3           0.6 0.2                                                 17         3           0.8                                                     18         3           0.8                                                     19         3           0.7 0.1                                                 20         3           0.8                                                     21         4               0.8                                                 22         2   1       0.5                                                     23                 1   1                                                       24     0.5 2.5                                                                 25     3       5               0.2                                             26         2.95        2                                                       27         1   2                                                               28             5                                                               29         1                                                                   30                                                                             31                 5                                                           32                 3                                                           33     2       4           2                                                   34         2                                                                   35     1               3                                                       36         5                   2                                               37         2.7                                                                 38     2.2     3                                                               39     5                                                                       40         2           0.8                                                     41                 4   0.8                                                     42                 4           0.8                                             43                     0.8                                                     44                     0.8                                                     45                     0.8                                                     46                     0.8                                                     47                     0.8                                                     48                     0.8                                                     49             2       0.8                                                     50     1.8     2       0.8                                                     51                     0.8                                                     52         1.8         0.8                                                     53             2       0.8                                                     54                     0.8                                                     55             1       0.8                                                     56                     0.8                                                     57     1.8     1       0.8                                                     58     1.8             0.8                                                     59     1.8             0.8                                                     60     2.8             0.8                                                     61         1.8         0.8                                                     62     1.8             0.8                                                     63     2.8             0.8                                                     No.                                                                               Sb.sub.2 O.sub.3                                                                   Nd.sub.2 O.sub.3                                                                   n.sub.2                                                                            σ                                                                            Da  Tg/LT                                                   __________________________________________________________________________     1      1.2 1.13                                                                               4.86                                                                               0.150                                                                              0.472                                                   2      1.2 1.13                                                                               4.87                                                                               0.150                                                                              0.481                                                   3      1.2 1.14                                                                               4.90                                                                               0.148                                                                              0.474                                                   4      1.2 1.14                                                                               5.02                                                                               0.145                                                                              0.474                                                   5      1.2 1.16                                                                               4.86                                                                               0.133                                                                              0.479                                                   6      1.2 1.20                                                                               4.83                                                                               0.135                                                                              0.462                                                   7      0.6 1.22                                                                               4.72                                                                               0.015                                                                              0.453                                                   8      0.6 1.28                                                                               4.89                                                                               0.293                                                                              0.462                                                   9  0.6 0.6 1.30                                                                               5.36                                                                               0.193                                                                              0.492                                                   10 0.6 0.6 1.28                                                                               5.32                                                                               0.182                                                                              0.520                                                   11     0.6 1.32                                                                               5.20                                                                               0.241                                                                              0.473                                                   12     0.6 1.31                                                                               5.15                                                                               0.239                                                                              0.480                                                   13     0.6 0.82                                                                               5.18                                                                               0.237                                                                              0.523                                                   14     1.2 1.26                                                                               5.23                                                                               0.145                                                                              0.482                                                   15     1.2 1.30                                                                               5.24                                                                               0.140                                                                              0.473                                                   16     1.2 1.28                                                                               4.93                                                                               0.130                                                                              0.492                                                   17     1.2 1.28                                                                               5.12                                                                               0.270                                                                              0.483                                                   18     1.2 1.29                                                                               5.27                                                                               0.350                                                                              0.475                                                   19     1.2 1.29                                                                               5.50                                                                               0.510                                                                              0.452                                                   20     1.2 1.30                                                                               5.72                                                                               0.553                                                                              0.450                                                   21     1.2 1.32                                                                               5.63                                                                               0.542                                                                              0.460                                                   22     0.3 1.27                                                                               6.10                                                                               0.92                                                                               0.453                                                   23     1.2 1.18                                                                               6.18                                                                               0.89                                                                               0.442                                                   24     1   1.25                                                                               5.70                                                                               0.80                                                                               0.462                                                   25     2.5 1.32                                                                               4.62                                                                               0.53                                                                               0.473                                                   26     0.05                                                                               1.01                                                                               5.02                                                                               0.13                                                                               0.489                                                   27     1.5 1.20                                                                               5.53                                                                               0.48                                                                               0.452                                                   28     1.3 1.19                                                                               5.42                                                                               0.40                                                                               0.456                                                   29     5   1.36                                                                               4.98                                                                               0.03                                                                               0.482                                                   30 0.3 2.5 1.25                                                                               5.24                                                                               0.22                                                                               0.470                                                   31 0.2 0.8 0.97                                                                               5.33                                                                               0.19                                                                               0.490                                                   32     3   0.89                                                                               4.49                                                                               0.11                                                                               0.523                                                   33     1.2 1.37                                                                               4.32                                                                               0.13                                                                               0.488                                                   34 0.5 1.4 1.23                                                                               5.98                                                                               0.73                                                                               0.471                                                   35     3   1.40                                                                               5.63                                                                               0.18                                                                               0.464                                                   36     2   1.38                                                                               4.39                                                                               0.02                                                                               0.487                                                   37 0.3 2   1.25                                                                               4.41                                                                               0.15                                                                               0.483                                                   38     1.8 1.24                                                                               5.20                                                                               0.37                                                                               0.477                                                   39     1.8 1.30                                                                               5.00                                                                               0.09                                                                               0.480                                                   40     1.2 1.26                                                                               5.26                                                                               0.21                                                                               0.475                                                   41     1.2 1.32                                                                               5.35                                                                               0.08                                                                               0.482                                                   42     1.2 1.35                                                                               5.12                                                                               0.06                                                                               0.497                                                   43     1.2 1.17                                                                               4.88                                                                               0.23                                                                               0.462                                                   44     1.2 1.09                                                                               4.95                                                                               0.25                                                                               0.451                                                   45     1.2 1.13                                                                               4.20                                                                               0.18                                                                               0.468                                                   46     1.2 1.18                                                                               4.83                                                                               0.31                                                                               0.472                                                   47     1.2 1.20                                                                               4.85                                                                               0.28                                                                               0.470                                                   48     1.2 1.15                                                                               4.89                                                                               0.30                                                                               0.463                                                   49     1.2 1.10                                                                               4.83                                                                               0.56                                                                               0.470                                                   50     1.2 1.12                                                                               5.26                                                                               0.29                                                                               0.482                                                   51     1.2 1.10                                                                               4.82                                                                               0.28                                                                               0.462                                                   52     1.2 1.15                                                                               5.27                                                                               0.37                                                                               0.468                                                   53     1.2 1.03                                                                               6.10                                                                               0.89                                                                               0.420                                                   54     1.2 1.04                                                                               5.83                                                                               0.87                                                                               0.420                                                   55     1.2 1.02                                                                               6.10                                                                               0.90                                                                               0.413                                                   56     1.2 1.03                                                                               5.94                                                                               0.90                                                                               0.410                                                   57     1.2 1.17                                                                               5.13                                                                               0.21                                                                               0.473                                                   58     1.2 1.20                                                                               5.37                                                                               0.26                                                                               0.470                                                   59     1.2 1.23                                                                               5.29                                                                               0.25                                                                               0.475                                                   60     1.2 1.26                                                                               5.48                                                                               0.15                                                                               0.482                                                   61     1.2 1.25                                                                               5.30                                                                               0.15                                                                               0.480                                                   62     1.2 1.21                                                                               5.56                                                                               0.24                                                                               0.479                                                   63     1.2 1.24                                                                               5.13                                                                               0.17                                                                               0.483                                                   __________________________________________________________________________

For the preparation of the phosphate base laser glasses of this invention as shown in the Table the components were sufficiently mixed, melted over a period of about 3 to about 5 hours and then refined at 1200°-1500° C. in a platinum crucible or a ceramic crucible, and, after homogenizing the melt by means of a stirrer at 900°-1100° C. for about 4 to about 10 hours, the melt was molded. As one skilled in the art will appreciate, at the time the materials are initially mixed they are not yet a "glass", but soon change from their initial powdery form to a sticky liquid form, and thereafter, with increased temperature, they yield a glass. All processings were, of course, at atmospheric pressure.

When the fluorides were used, it was necessary to melt and refine the mixture at 800°-1100° C. so that the fluorine did not volatilize off during melting. Also, since fluorides tend to form striae in the glass, the melting and molding of the mixture containing the fluorides were conducted with care.

Thereafter, the glass molding was subjected to precise annealing to remove residual strain to provide a large laser glass free of strain. Annealing was conducted by first setting the temperature at about 450° C. and then cooling at a rate of about 0.25° to about 0.50° C./hour.

While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof. 

What is claimed is:
 1. A phosphate base laser glass possessing an induced emission cross section σ of 4.50 to 5.20×10⁻²⁰ cm², a non-linear refractive index coefficient n₂ of 1.13 to 1.24×10⁻¹³ e.s.u., an acid resistance weight loss Da of 0.15 to 0.17% by weight and a devitrification resistance Tg/LT of 0.470 to 0.485, consisting of(i) 58 to 67% P₂ O₅, (ii) 4 to 10% Al₂ O₃, (iii) 9 to 15% Li₂ O, (iv) 4 to 10% Na₂ O, (v) 0 to 12% CaO, 0 to 12% MgO, 0 to 12% CaF₂, 0 to 12% MgF₂, the total proportion of said CaO, MgO, CaF₂ and MgF₂ being 5 to 12%, (vi) 0 to 3% Y₂ O₃, (vii) 0.2 to 0.8% Nb₂ O₅, and (viii) 0.2 to 1.5% Nd₂ O₃,said percentages being by mole.
 2. The phosphate base laser glass as claimed in claim 1 wherein one or more of Li₂ O, Na₂ O, or Al₂ O₃ is partially or wholely replaced by LiF, NaF, or AlF₃, respectively.
 3. The phosphate base laser glass as claimed in claim 1, wherein the mole percent of Li₂ O is greater than the mole percent of Na₂ O. 